@jjrochow@ra.rockwell.com - 4 reasons:1) New architecture. Does things other architecures don't, lots of new hardware logic.2) Proprietary machine language - Any translation from a current Forth would practically be a write from scratch anyway.3) Different operators - I'm used to C, so as much as possible I am changing standard Forth ops to their C equivalents. Might as well piss off all the Forth user groups at the same time!4) I'm interested in HLL design generally, so starting from scratch is the best way for me to learn anyway.

@RajuK- Compring compilers is difficult. There are some benchmarks, but usually the benchmarks are so different from you own application that they are not a good predictor. Mostly you learn from experience or from other engineers... Optimizing compilers tend to be better, but they can also cost alot more...

@gamatec- Superscaler processors typically execute multiple instructions at a time. For example, they can do a logical operation, and arithmetic operation at the same time. This is possible because the have multiple execution units (multiple ALus for example).

Response to earlier question: Do you typically have a tight 'inner loop' in your algorithms that is critical for high-performance? Have done so on occassion, but typically rely on a main loop and interrupts.

Response to earlier question: Do you typically start a design with existing code in place or start from 'scratch'? Depends on the assignment. I have worked both to complete other designs, and on new designs from scratch.

@Dev.khan- These days the embedded industry is looking for embedded programmers with experience in specific algorithms (as well as a track record of successful designs). Motor control for example is a popular algorithm...

@Dev.khan- I don't have any specific recommendations for a book on CM-3. Check out the MCU site however or go over to Microcontroller Central and ask a question on the site. That might give you some ideas.

There is a feature call 'Isochonous Operation' which means clock/synchronous I/O for the PLC. The overall module loop has a very tight timing requirement. The interrupts are usually handled with assembly and many of the control processes are handled with assembly in order to meet very strict timing.

I am typically leveraging on existing code. Typically I am pulling from two or three sources merging source as well. Mixed assembly and C code, and at times I have to try and translate between assembly source based on the used MCU.

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@Mark.Browne- Excellent point about compilers with multiple MCU targets. Some of the optimizing compilers can eliminate the more 'generic' code that gets generated but the 'simple' compilers we get for free from the MCU manufacturers may not have these features available. (You might need to pay for them).

Development Tools: Perhaps the best way to start out is to use the MCU manufacturers free tools- either an evaluation version of a 3rd party tool or the MCU manufacturers own version. That way you can try it out before purchasing something. Check out the website of the MCU manufacturer you are targeting and you will usually find the tools right away.

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Oops - I should add that stack frame addressing is not very efficient with the Z80. This speaks to the general case that complier writers are likely to use the same general methods for all the compilers they make. If one of the targets does not implement that method very well the generated code is likely to suffer.

I should add that stack frame addressing is not very efficient with the Z80. This speaks to the general case that complier writers are likely to use the same general methods for all the compilers they make. If one of the targets does not implement method that very well the generated code is likely to suffer.

@Mark.Browne- Thanx for the decription. Uniform calling conventions can add some overhead so that is a good one to look at. More modern optimizing compilers might catch some of these inefficiencies, but it is still good to keep them in mind, and to look at your generated code once in a while to see what improvements have been made. I will bring this point up in todays class. Thanx!

This was an older compiler so I am not sure if it still relevant today.

That said - There was much data movement to and from the stack to support uniform calling conventions. There was a good deal of promotion and testing to 16 bit that was not strictly needed; I suspect that modern optimizing compliers don't do this.

@Mark.Browne- Doing that type of comparison is very valuable. Did you notice any particular areas (types of functions) where your C implementation was particularly inefficient with respect to code size?

After a large project writing assembly language to interface with existing C code and replace some C code. This was due to severe space constraints; I was able to get about a 10% code shrink which allowed the needed code enhancements to fit in the ROM. As I went through each routine I could see how each C token was implemented in assembly language by the compiler. It was a most educational process. I can now see what C does and how it does it; I think of C as pretty assembly language.

@wonohkim, not true. Yes C and assembly are the popular languages for MCU because they simply are the most commonly supported, but there are several languages that support control register and memory maps.

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It won't be too much longer and hardware design, as we used to know it, will be remembered alongside the slide rule and the Karnaugh map. You will need to move beyond those familiar bits and bytes into the new world of software centric design.

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